The present invention relates to a hydraulic braking system and more particularly to a multiple pressure input braking system where the front brakes are pressure referenced to the rear brakes.
The present invention is directed to a novel braking system in which the front brake pressure is alternatively controlled by master cylinder pressure or referenced to the rear brake pressure and generated by an electrically controlled pump. In this system the rear brake pressure is used as the control signal for the front brakes.
It is the object of the present invention to provide a hybrid type of brake actuation system wherein the front brakes are referenced to the brake pressure communicated to the rear brakes.
Accordingly, the invention comprises: a braking system, including: a master cylinder; rear brakes communicated to the master cylinder; front brakes hydraulically isolated from the rear brakes. An isolation valve interposes the master cylinder and the front brakes and has a first operative state communicating the master cylinder to the front brakes and a second state isolating the master cylinder from the front brakes. The system additionally includes a pump for activating the isolation valve and for pressurizing the front brakes. A motor is employed to power the pump and control unit means are used to cause the front brake pressure to follow rear brake pressure. The control unit means is responsive to a first pressure signal indicative of rear brake pressure and a second pressure signal indicative of the front brake pressure. The control unit comprises electric proportioning means for generating a commanded front brake pressure signal (P.sub.C), comparison means for comparing the command brake pressure signal to the actual brake pressure signal and for generating an error signal (P.sub.E); motor control means responsive to a positive error signal for activating the motor and for powering the pump (42). The system further includes means for normalizing the operating of the front and rear brakes and more specifically includes means for time delaying the operating of the rear brakes. This is accomplished by including in the rear brake line a flow restriction or orifice in parallel with a check valve. In an alternate embodiment of the invention an electrically operated isolation valve and a dump or relief valve is used.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.